How fast is the player able to travel? Are there ways they can travel faster if they just want to get somewhere quickly, or are they stuck with a single speed?

Will there be any time limits or pressure to reach destinations quickly?

Do you want the player to carefully explore zones, or is it more likely they'll only see some of the content?

Do you have interesting content to fill the zone, or will there be a lot of "dead" space?

Players generally don't like "dead" or pointless space, so if there isn't a meaningful reason for zones to be large consider reducing the size.

You know how fast your players are able to travel. Given those speeds, how far can they travel within any time limits you might be imposing? By making them travel farther in a shorter time you increase pressure, especially if there's the chance of taking a sub-optimal or dead-end path. By choosing distances in which they can easily reach destinations quickly you create a lower pressure situation more conducive to exploration and wandering.